Prostaglandins are acidic lipids derived from the metabolism of arachidonic acid by the action of cyclooxygenase enzymes and downstream synthases. Prostaglandins have a diverse range of activities and have a well recognized role in a variety of disease or conditions, such as allergic diseases or conditions, inflammatory diseases or conditions, and respiratory diseases or conditions. Prostaglandin D2 (PGD2) is an acidic lipid mediator derived from the metabolism of arachidonic acid by cyclooxygenases and PGD2 synthases. PGD2 is produced by mast cells, macrophages and Th2 lymphocytes in response to local tissue damage as well as allergic inflammation in diseases such as asthma, rhinitis, and atopic dermatitis. Exogenous PGD2 applied to bronchial airways elucidates many characteristics of an asthmatic response suggesting that PGD2 plays an important pro-inflammatory role in allergic diseases.
PGD2 binds to a number of receptors, which include the thromboxane-type prostanoid (TP) receptor, PGD2 receptor (DP, also known as DP1) and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2; also known as DP2). DP2 is associated with promoting chemotaxis and activation of Th2 lymphocytes, eosinophils and basophils. In particular, PGD2 binds to DP2, and mediates its effects through a Gi-dependant elevation in calcium levels and reduction of intracellular cyclic AMP. In Th2 lymphocytes, IL4, IL5 and IL13 cytokine production is stimulated. These cytokines have been implicated in numerous biological actions including, by way of example only, immunoglobulin E production, airway response, mucous secretion, and eosinophil recruitment.